The invention relates to a method and an apparatus for selecting a transmission channel in a network radio link. The invention relates particularly to the selection of a transmission channel or of a connecting network in a wireless communication network on the basis of a multiantenna transmission method in which radio signals are transmitted between at least one radio base station and a mobile terminal, which have at least two antennas. The invention additionally relates particularly to the selection of a radio transmission channel from a plurality of radio channels that each have different transmission technologies.
Selection of the transmission channel or of the connecting network in a mobile radio network involves regularly deciding on the static base station with which a mobile radio, for example a cellphone, communicates for data transmission. By way of example, a change of transmission channel can become necessary when the mobile radio is in an area in which signals from two base stations can be received. In particular, this is necessary, by way of example, when the mobile radio moves from the transmission/reception area, i.e. mobile radio cell, of the first base station into the transmission/reception area of the second base station, for example on a car journey. The change in the communication of the mobile radio from the transmission channel with the first base station to the transmission channel with the second base station is also called a handover process.
US 2009/0059861 A1 describes various methods for controlling a handover process in a cell-based transmission system with a change between two transmission frequencies. In a first method, the signal strength on the respective transmission frequency is ascertained on the mobile radio and the connection is set up using that frequency that has the higher signal strength. In a second method, the signal quality of the respective transmission frequency is ascertained on the mobile radio and the connection is set up using the transmission frequency with the better signal quality.
US 2011/0267969 A1 likewise describes a handover process between mobile radio cells, in which a series of received signal parameters are used for controlling the process, such as signal strength and signal-to-noise ratio.
Mobile terminals such as cellphones, smartphones, tablet PCs or laptops are additionally increasingly able to communicate, in particular wirelessly, using different communication systems, in particular wirelessly using radio channels of different transmission technologies. To this end, they are linked to appropriate electronic communication-system-specific components or technologies and, to this end, have electronic components corresponding to the respective technology. By way of example, one first such communication system technology is a mobile radio technology for data transmission on the basis of corresponding mobile radio standards, such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications Systems (UMTS) or Long Term Evolution (LTE). A further wireless transmission technology is a technology for operating a computer network, particularly for a wireless local area network (WLAN) based on the IEEE 802.11x standard. By way of example, a further wireless transmission technology for mobile terminals is Bluetooth technology based on the technological standard IEEE 802.15.1. Different transmission technologies can have different transmission frequencies, for example. To control the respective data transmission, a respective appropriate, standardized transmission protocol is provided for the transmission technologies, with different versions of the standard being able to be provided in each case, such as GSM 2G/3G or IEEE 802.11a/b/n, which each have different details for the respective implementations.
Selection of the transmission channel or of the connecting network in a mobile radio network involves regularly deciding on the static base station with which a mobile radio, for example a cellphone, communicates for data transmission. By way of example, a change of transmission channel can become necessary when the mobile radio is in an area in which signals from two base stations can be received. In particular, this is necessary, by way of example, when the mobile radio moves from the transmission/reception area, i.e. mobile radio cell, of the first base station into the transmission/reception area of the second base station, for example on a car journey. The change in the communication of the mobile radio from the transmission channel with the first base station to the transmission channel with the second base station and/or between mobile radio networks or transmission channels is also called a horizontal handover process.
In what are known as hybrid communication networks, a wireless data link can be provided using radio channels of different transmission technologies and/or using different connection infrastructure components.
In hybrid communication networks, it is sometimes advantageous or even necessary to change over the wireless data link between terminals, base stations, switching centers and/or central data sources between radio channels of different transmission technologies selectively and/or in parallel, entirely or partly and permanently or temporarily. In order to be able to control such, what are known as vertical, handover processes automatically and to make the associated decisions in hybrid communication networks advantageously, suitable decision criteria or algorithms are needed. In hybrid communication networks, it is sometimes also advantageous or even necessary to change over the wireless data link between terminals, base stations, switching centers and/or central data sources between radio channels with a different connection infrastructure in the same transmission technology, for example between infrastructure components of different mobile radio providers or between base stations of different mobile radio cells, selectively and/or in parallel, entirely or partly and permanently or temporarily. In order to be able to control such horizontal handover processes automatically and to make the associated decisions in hybrid communication networks advantageously, suitable decision criteria or algorithms are likewise needed.
The ever more widespread, parallel availability of static or mobile network elements of different connection technologies, such as WLAN elements, for example on the basis of the IEEE 802.11x or ETSI ITS G5 standard, or mobile radio networks, using multiantenna radio, such as on the basis of the 3GPP LTE standard, results in ever more networking options for connecting the mobile terminal to a central device (what is known as a backend).
It is a first possible object of the invention, for communication systems that have a multiantenna network radio link that can be used transmit data by means of radio signals between at least one radio base station and a mobile terminal, which each have at least two antennas, to allow the transmission channel to be selected such that a high connection quality is achieved.
It is a second possible object of the invention, in a communication network that allows a wireless data link using radio channels of different transmission technologies and/or different infrastructure components, to achieve a high connection quality.
At least one of these objects is respectively achieved by the invention specified in the independent patent claims. Advantageous embodiments of the invention are respectively specified in the dependent claims.
According to a first aspect of the invention, transmission channel selection in a network radio link in which data are transmitted by means of radio signals between a radio base station and a mobile terminal has provision for the radio base station and the mobile terminal to each have at least two antennas that form a plurality of transmission paths for the radio link and at least two transmission channels for the data transmission, which each use one or more of the transmission paths in accordance with a channel matrix,                the mobile terminal to have at least one decoder that can be used to decode radio signals received from at least one of the terminal antennas to obtain the data, and        the transmission channel selection to be used to decide which instance(s) of the transmission paths and/or which communication system technology is/are used to transmit the data between radio base station and mobile terminal.        
In this case, there is provision for the following steps:                the mobile radio base station uses the transmission paths to transmit mobile radio signals for first data to the mobile terminal using at least one communication system technology,        the mobile radio signals are supplied to the decoder on a transmission-channel-by-transmission-channel basis,        the decoder decodes the mobile radio signals and in so doing obtains the first data on a transmission-channel-by-transmission-channel basis,        the decoded first data are used on a transmission-channel-by-transmission-channel basis to form at least one quality value that is representative of a quality of the data transmission via the respective transmission channel, and        a comparison of the quality values of the transmission channels is used to perform the transmission channel selection for the subsequent transmission of second data that form useful data.        
The first aspect of the invention is based on the insight that, for optimum selection of the respective transmission channel, it is more beneficial to determine channel-specific quality values than just signal-specific values such as power level or signal-to-noise ratio. The invention is also based on the insight that the transmission channel selection on the basis of channel-specific quality values is particularly advantageous when the mobile terminal has at least two antennas.
In this case, the physical proximity of the reception antennas means that the signal-specific values frequently differ less than channel-specific quality values, which are also dependent on other factors, such as the communication system technology used on the respective channel.
This aspect of the invention has additionally been used to identify that transmission channel selection on the basis of the quality value allows more efficient utilization of radio resources than when the transmission channel selection is made on the basis of power-oriented threshold value decisions, because the powers are frequently dependent on spatial influences such as reflection, diffraction and/or scatter of the electromagnetic waves. The approach according to the invention can have an effect at the terminal in the form of increased functional quality and at the network operator by virtue of improved use of the available spectral efficiency, i.e. a greater transmittable volume of information per time and per hertz of bandwidth. In addition, the invention can advantageously be used to increase the robustness of the radio link and to increase the transmission capacity and the range between infrastructure and mobile terminal. The terminal can furthermore advantageously reduce the power draw required and hence possibly increase the operating time of the storage battery.
In an advantageous exemplary embodiment of the first aspect of the invention, at least one antenna of the radio base station and one antenna of the mobile terminal are set up to transmit data on the basis of at least two different communication system technologies. One or more of the antennas can be used for two communication system technologies, e.g. for the GSM and LTE technologies, simultaneously or in parallel. The mobile terminal can particularly have at least two antennas for different communication system technologies.
The quality value can be formed on the basis of physical properties of the transmission path and/or of the channel and particularly from weighted channel parameters. To this end, there are a multiplicity of suitable physical variables, of which, merely by way of example, the absolute data transmission rate attained via the path or channel, a condition number—ascertained on the basis of the channel matrix—of the transmission channel and/or the spectral efficiency of the path or channel may be cited here.
For the decision about which transmission channel is used, a transmission matrix having associated channel parameters can be formed for a plurality of available transmission channels, particularly for preselected channels or for all channels available in the radio link. The transmission or channel matrix can comprise complex channel weights between all combinations of transmission and reception antennas in a multiantenna transmission system. In a 2×2 transmission system having two transmission antennas and two reception antennas, a total of four complex transmission parameters then need to be evaluated, for example.
The invention particularly allows vertical handover decisions in hybrid communication networks to be made advantageously, these involving deciding which radio transmission standard connected to the transmission channel and/or which communication system technology is/are used to transmit useful data between mobile radio base station and mobile terminal. The ever more widespread, parallel availability of static or mobile network elements of different connection technologies, such as WLAN elements, for example on the basis of the IEEE 802.11x or ETSI ITS G5 standard, or mobile radio networks having multiantenna radios, such as on the basis of the 3GPP LTE standard, results in ever more networking options for connecting the mobile terminal to a central device (what is known as a backend). According to the invention, it has been identified that better transmission properties can be achieved for such radio networks by virtue of physical channel properties instead of purely power-based channel parameters being taken into account for the selection of the transmission channel, including the associated communication system technology and/or the associated radio transmission standard, i.e. for a vertical handover decision.
Determining the quality value can involve channel parameters of the transmission matrix being ascertained. In an advantageous exemplary embodiment of the invention, determining the quality value can involve channel estimation being performed. To this end, by way of example, channel parameters of the transmission matrix can be estimated on the terminal at the output of the decoder that decodes the respective radio signals. By way of example, channel parameters are estimated on the basis of analysis values from a communication modem that has a finite bandwidth with a finite measuring time and a finite resolution. By way of example, the channel estimation can comprise integration, in particular short-term integration, over a prescribed, limited reception bandwidth and a finite measuring time, for example over at least a portion of a preamble, i.e. over a known bit sequence of a transmission protocol used for the radio link, and/or other parameters of the respective network, particularly on the physical network level (PHY) thereof in the OSI (Open Systems Interconnection Model) layer model. In particular, the quality value can be used in order to be able to take account of channel influences on the data transmission for the demodulation of the received radio signals during channel selection. To this end, the channel estimation can be performed, in particular regularly, according to prescribed rules, for example at regular intervals of time. On the basis of this channel information, extended rating of the radio network quality is possible, with purely passive rating of the transmission parameters being able to be performed by the mobile terminal. This means that no additional system bandwidth is necessary.
The improved assessment that the invention allows for the radio network quality or quality of the transmission channel can advantageously be used for vertical handover decisions when the connection technology is changed between radio base station or infrastructure and mobile terminal. This results in a higher data transmission rate and in greater robustness of the data transmission. The improved assessment of the radio network quality or transmission channel quality can additionally be used for deriving horizontal handover decisions, that is to say for changing between two networks of the same connection technology, that is to say when changing between overlapping or adjoining mobile radio cells of the same mobile radio standard, such as GSM, or between two WLAN networks, for example. The invention therefore allows advantageous dual use of the available information about the quality of the respective transmission channel or radio network.
The first aspect of the invention allows the following further advantages to be achieved:                The transmission capacity can be increased despite a comparatively low reception power level on the mobile terminal.        Increased robustness of the radio link for provision of the same functional quality for comparatively low reception power levels on the mobile terminal.        Increased range of the radio system for constant functional quality.        Compensation for transmission imbalances owing to different antenna locations or different antenna efficiencies, for example, through evaluation of the information from the entire channel matrix.        
According to a second aspect of the invention, which can be implemented in combination with the first aspect of the invention or else independently thereof, a radio transmission channel is selected from a group of radio transmission channels, which each correspond to different transmission technologies and/or use different infrastructure components, in order to set up a data link between a mobile unit and a central unit. In this case, the central unit can be connected, and in particular is connected, to a first local unit that is arranged in a regional area and that can be used to set up a data transmission link to the mobile unit by means of a first radio transmission channel that corresponds to a first transmission technology from the different transmission technologies and/or uses a first infrastructure component. In addition, the central unit can be connected, and in particular is connected, to a second local unit that is arranged in a regional area and that can be used to set up a connection to the mobile unit by means of a second radio transmission channel that corresponds to a second transmission technology from the different transmission technologies and/or uses a second infrastructure component. The mobile unit has at least two radio units that are each designed for data transmission using one of the two radio transmission channels. The radio transmission channel is selected from the group of radio transmission channels by means of control data that are produced and/or stored outside the mobile unit. They can be transmitted particularly from an external data source to the mobile unit in order to control the selection. Following the selection, the data connection can be set up between the mobile unit and the central unit using the selected radio transmission channel.
The radio transmission channel is selected particularly in a communication network in which the data link is set up. The selection can be made in the mobile unit and particularly when the mobile unit is in the regional area or moves toward this area, in which a connection both to the first local unit and to the second local unit can be set up by means of its at least two radio units. The selection can be made particularly in the course of the change from a first regional area to a second regional area, with the radio transmission channel being able to be changed or changed over in the mobile unit depending on the selection. On the basis of the selection, a horizontal and/or vertical handover process can be performed for the radio transmission channel. To this end, the radio units may each be of corresponding design, for example by virtue of a transmission and/or reception unit that corresponds to a respective radio transmission technology and/or by virtue of an electronic and/or program-oriented component that can be used to provide coupling to an infrastructure component of the communication network, for example a SIM mobile radio card.
The selection of the radio transmission channel from the group of radio transmission channels can be made entirely or partly automatically. By way of example, it can be controlled entirely or partly by a computer program that is executed by means of a processor provided inside the mobile unit. The selection can also be controlled by suitable other electronic and, in particular, digital control components.
In an advantageous exemplary embodiment of the second aspect of the invention, the control data are produced, provided and/or transmitted to the mobile unit by the central unit and/or at least one of the local units. The radio transmission channel can be selected in the mobile unit, in particular. Selection of the radio transmission channel can involve the interaction of a controller provided in the mobile unit, a controller provided in the central unit and/or a controller provided in one of the local units. The mobile unit may be a vehicle, in particular.
According to a third aspect of the invention, which can be implemented alone or in combination with at least one of the other two aspects of the invention, a radio transmission channel is selected from a group of radio transmission channels, which each correspond to different transmission technologies and/or use different infrastructure components, in order to set up a data link between a mobile unit and a central unit. In this case, the central unit can be connected, and in particular is connected, to a first local unit that is arranged in a regional area and that can be used to set up a data transmission link to the mobile unit by means of a first radio transmission channel that corresponds to a first transmission technology from the different transmission technologies and/or uses a first infrastructure component. In addition, the central unit can be connected, and in particular is connected, to a second local unit that is arranged in the regional area and that can be used to set up a connection to the mobile unit by means of a second radio transmission channel that corresponds to a second transmission technology from the different transmission technologies and/or uses a second infrastructure component. The mobile unit has at least two radio units that are each designed for data transmission using one of the two radio transmission channels. The selection of the radio transmission channel from the group of radio transmission channels involves the use of data pertaining to at least one earlier radio link, what are known as historical data, for at least one of the radio transmission channels in the regional area. The data link can then be setup between the mobile unit and the central unit using the selected radio transmission channel.
In particular, the historical data can be obtained empirically and/or can be data provided with time stamps and/or stored. In particular, the historical data can be captured, provided and/or stored in the mobile unit, in at least one of the local units, in the central unit and/or in a further data source, for example in a backend server that can be connected to the communication network, and in particular may be invariably available therein. In particular, the historical data can be interchanged between one or more of these units. The mobile unit is mobile and moves particularly in the regional area.
By way of example, the infrastructure component may be a mobile radio base station, a central unit of a network operator or a control component of the respective communication network, particularly of the mobile radio network of the network operator. The infrastructure component may also be an appropriate component for a radio transmission channel of a different transmission technology, for example an access point for a WLAN network.
The third aspect of the invention is based on the insight that the selection process for a radio transmission channel in a regional area can be controlled much more simply and accurately if what are known as external control data, which are produced and/or stored outside the mobile unit, are available and used for at least one of the radio transmission channels in the regional area. The selection decision can then be made on the basis of a broader information base, particularly when both external control data and internal data produced or available inside the mobile unit, for example sensor data pertaining to the reception strength of the radio transmission channel, are used. This can result in a series of advantages, particularly for selection decisions for vertical and/or horizontal handovers in hybrid networks:                High connection quality, particularly when both internal and external data are available and are used. The connection quality can have the effect of fail-safety for the radio link, fast connection setup and/or inexpensive connection, for example.        High reception strength, particularly when external data pertaining to the reception strength of a plurality of radio transmission channels are used for controlling the channel selection.        No or fewer connection interruptions and relatively few vertical handover events and therefore more robust communication. This is of great importance particularly when the mobile unit is moved, for example as a smart phone with a vehicle and particularly in the form of a vehicle, for example when a mobile radio card is permanently integrated in the vehicle.        Short connection time (what is known as air time) between the mobile unit and the local unit. This allows more efficient use of the radio transmission channel, avoidance of unnecessary protocol overhead for the communication thereof and optimization of resources of the radio interface.        
In particular, provision may be made for at least one of the units, preferably the mobile unit, to contain at least one sensor that is used to capture measured values from the respective radio transmission channel that are definitive for the quality of the radio transmission, said measured values likewise being used for selecting the radio transmission channel. By way of example, the sensor(s) can be used to capture the following measured variables:                Passively measurable network parameters such as performance characteristics, reception strength, signal-to-noise ratio, channel load, interference behavior, etc.        Actively measurable network parameters such as latency, packet error rate or maximum or average data transmission rate.        
In particular, the sensor may be integrated in the mobile radio modem or the mobile radio modem itself may be the sensor.
Further local measured variables that are, in particular, not network-specific or not specific to the radio transmission channel and/or are recorded by vehicle sensors can be captured, particularly in the mobile unit, and used for the selection, for example by means of position, direction, speed and acceleration sensors, rotation rate sensors, direction sensors, imaging sensors, weather sensors, particularly precipitation sensors, etc.
According to an advantageous exemplary embodiment of the invention, the historical data and/or the external control data are geodata-referenced and the radio transmission channel is selected on the basis of position finding for the mobile unit and the geodata-referenced historical data. In this case, it is furthermore advantageously possible for position finding for the mobile unit to be performed by means of a navigation system and for a route that is stored in the navigation system and along which the mobile unit moves and the geodata-referenced historical data to be used for preconditioning the respective selection process for the radio transmission channel for road sections along the route. The historical data may also be time-referenced and the selection can be made on the basis of timing and the time-referenced historical data.
Criteria for the selection of the radio transmission channel or associated data transmission network can be determined both locally in the mobile unit on the basis of values ascertained by measurement and/or scanned and cooperatively. In the case of cooperative determination, data about radio transmission channels can also be received and used from other data sources, such as the local units or from a central data service, particularly from the central unit. Historical data and/or up-to-date data pertaining to the respective data transmission networks and/or technologies can be provided as what is known as an availability map, which comprises a plurality of local areas, is time-referenced and/or is created by the mobile unit or an external data source of the network provider or other service provider. In addition, it is particularly possible for a network operator to provide a network utilization map that shows the present utilization of the respective network or of the respective radio transmission technology. On the basis of the availability map and/or the network utilization map, a know-how map can be created that comprises additional data, empirical values and/or ratings and, in particular, historical data. The relevant historical data are each based on a multiplicity of data ascertained empirically and particularly by measurement, for example pertaining to network availability, pertaining to the availability of the respective transmission technology and/or pertaining to the respective signal strength. Data from the availability map, the network utilization map and/or the know-how map can be used to select the radio transmission channel and/or a network infrastructure component. By way of example, the position sensors may be geodata-referencing sensors based on the global positioning system (GPS).
The mobile unit or the mobile terminal may particularly be a vehicle. A vehicle within the meaning of the present invention can be any type of vehicle, for example a bicycle, a motor vehicle, an electric vehicle, a train, a ship, etc. The mobile unit may also be a mobile radio, such as a smartphone, or another unit that comprises at least one electronic communication module.
Said measured variables can be used advantageously particularly when the mobile unit is a vehicle or is used in the course of movement in a vehicle. In this case, local vehicle parameters can be captured as measured variables and used for selecting the radio transmission channel.
The use of up-to-date measured variables from the vehicle sensors and/or of corresponding up-to-date data from other sources for selecting the radio transmission channel allows improved preconditioning, particularly for vertical and/or horizontal handover decisions, for weather influences, such as snowfall or heavy rain, or for high road traffic volumes. Such preconditioning allows, in particular, vertical and/or horizontal handover decisions that are made for a moving mobile unit in the course of a transfer between two mobile radio cells to be improved.
According to a further advantageous exemplary embodiment of the invention, selection of the radio transmission channel involves the interaction of a controller provided in the mobile unit, a controller provided in the central unit and/or a controller provided in one of the local units.
The historical data and/or the external control data can be stored, in particular entirely or partly, in one of the controllers. They can be transmitted from this controller to another controller in the course of the selection process for the radio transmission channel.
The mobile unit can preferably contain a first control component for controlling the radio link of the first radio technology and/or for using the first infrastructure component, and a second control component for controlling the radio link for the second radio technology and/or for using the second infrastructure component. The two control components can interact for selecting the radio transmission channel for control purposes. The historical data are stored particularly in the mobile unit. These stored data are used particularly for selecting the radio transmission channel.
According to a further preferred embodiment of the invention, the radio transmission channel is additionally selected on the basis of at least one computer-controlled application that is executed on a processor that is connected to the mobile unit for control purposes and is particularly integrated in the mobile unit. By way of example, this embodiment can be used particularly advantageously when the mobile unit is a vehicle. Depending on the type of the at least one application, it is then possible for at least one of the radio transmission channels to be preferred in the selection. This allows optimization of the respective connection technology and/or infrastructure components for the respective application and hence optimization of the quality of the respective service provided by the application. By way of example, provision may be made for a radio transmission channel that can be used to transmit a high data rate, e.g. a WLAN channel, to be preferred for an entertainment application, while a radio channel with the highest possible signal strength, e.g. a GSM channel, is preferred for a safety-relevant application, for example, such as an emergency function. For the degree of preference, a parameter may be provided in corresponding decision algorithms for selecting the radio transmission channel, for example. The respective applications can also be categorized for the selection in respect of a priority. To this end, the emergency function and functions of driver assistance systems that are used to transmit traffic-flow-relevant data such as queue end data or cross traffic data can be ranked with a high priority, for example, while internet and multimedia functions are ranked with a medium priority and information services with low priority.
The application-oriented optimization for the selection of the radio transmission channel can be performed on the basis of locally captured and stored data within the mobile unit and/or on the basis of data that are provided by the central unit and/or transmitted to the mobile unit. In this case, the data can comprise historical data and/or further control data. By way of example, the decision parameters or optimization aims used for selecting the radio transmission channel can be the maximum data rate, a minimum transmission time, minimum transmission costs or maximum robustness of the respective data service.
The invention advantageously also allows the utilization or scaling of the various radio transmission channels to be optimized for a regional area, for example if the historical data reveal that a particular radio transmission channel is overloaded on a daily basis at a particular time, such as during “rush hour” in commuter traffic in the regional area, owing to the multiplicity of parallel users, and another radio transmission channel has only low utilization. In this situation, the historical data can be used to specifically select the radio transmission channel with little utilization, i.e. load balancing between the various radio transmission channels, such as a GSM mobile radio transmission channel and a WLAN radio transmission channel, can be performed in the regional area. This allows an increase in the spectral efficiency of the radio transmission channels in this area. Up-to-date data pertaining to rush hours or pertaining to traffic congestion or queues caused in some other way can also be provided in up-to-date fashion via the central unit and/or external data sources and used for selecting the radio link channel. To provide appropriate data, it is also possible to use what are known as crowd sourcing methods, where data are transmitted from a multiplicity of vehicles that are, or were recently, in the same regional area via a central data source, such as what is known as a backend server, or also directly from vehicle to vehicle, to the respective mobile unit in which the selection of the radio transmission channel is intended to be made.
Control data and/or historical data can also be transmitted directly from a first vehicle, which is particularly leaving the regional area, to a second vehicle, which is particularly entering the regional area, for example wirelessly in the form of a vehicle-to-vehicle (car-to-car) communication. These highly up-to-date data can then be used by the second vehicle for selecting the radio transmission channel.
When a radio transmission channel is used to perform a multiplicity of data transmissions in parallel, it is additionally advantageous to provide a central controller that takes account of the respective data-transmitting applications. This controller may be provided entirely or partly in the mobile unit, in the local unit and/or in the central unit. In this case, it is advantageous if measured variables ascertained locally with the mobile unit or the local unit are made available to the respective other units via suitable interfaces, for example via one or more of the radio transmission channels.
In cases in which the mobile unit is a vehicle, the invention can also be used particularly advantageously by virtue of said mobile unit also being able to be connected to a backend server by the radio transmission channels and the central unit and in turn being able to be connected to a multiplicity of other vehicles via this server for data purposes. It can therefore capture and store a multiplicity of historical data that are transmitted to it by the respective vehicles from the respective regional areas, for example pertaining to the radio transmission channels there. In this case, the transmitted data may be georeferenced, in particular, or can be georeferenced in the course of storage in the backend server.
For the selection of the radio transmission channel, it is possible to implement different algorithms that use the historical data and if need be further data or parameters and the classification, weighting and logic combination thereof. For corresponding decisions within the selection process, it is possible to use threshold-value-based rules, fuzzy-logic-based algorithms and/or algorithms that are based on the analytic hierarchy process (AHP) method, for example.
According to a further advantageous exemplary embodiment of the invention, channel connection data, what are known as external channel connection data, are produced for at least one data transmission process via one of the radio transmission channels in the regional area and outside the mobile unit. The radio transmission channel can then be selected from the group of radio transmission channels by means of the external channel connection data. In addition, the radio transmission channel can be selected particularly in the mobile unit.
A transmission technology within the meaning of the present invention can provide particularly a cellular network, at least one access point and/or at least one ad-hoc radio network. The transmission technology can correspond to a corresponding technological standard for data transmission, for example one of the standards                Global System for Mobile Communications (GSM), GSM2, GSM3 (Universal Mobile Telecommunications System, UMTS), GSM4 (Long Term Evolution, LTE, LTE-A),        Wireless Local Area Network (WLAN) based on the group of IEEE 802.11x standards,        the European Telecommunications Standards Institute Intelligent Transport System standard ETSI ITS G5, or        the Worldwide Interoperability for Microwave Access (WiMAX) standard, and if need be in turn a particular version thereof and standards derived therefrom, or        another data transmission standard.        
The corresponding radio base station may be a mobile radio base station or a WLAN network router or a WLAN Access Point, for example. The communication system technologies of the antennas may each be designed accordingly.
An antenna can be used exclusively for data transmission on the basis of a particular communication system technology or nonexclusively, the antenna then being jointly used for data transmission on the basis of further communication system technology. By way of example, an antenna in an antenna array or in an antenna arrangement comprising at least two antennas can be used either in the complex for data transmission on the basis of a multiantenna communication system technology, such as LTE technology, or individually for transmission on the basis of a single-antenna technology, such as GSM technology.
The invention can advantageously be used for control-oriented coordination between controllers of different radio transmission channels or communication technologies and/or infrastructure components. A selection method according to the invention for a radio transmission channel allows active resource management and active connection management for the respective radio transmission channels to be performed, particularly by the mobile unit. These may be application-based, in particular. They can be controlled centrally. In addition, a specific cost function can advantageously be used to achieve optimized handling of the available degrees of freedom in a hybrid network and hence an improvement in the functional quality during use thereof. The specific selection of the radio transmission channel also allows the energy efficiency of the mobile unit to be improved, for example by virtue of the reduced transmission power being able to be set for the radio transmission channel or a radio transmission channel having less complex signal processing effort being selected.
The invention particularly also allows connection charges for the data link between the mobile unit and the central unit to be saved if the external data contain a charge parameter that corresponds to the charge tariffs respectively associated with the regional area and/or with the time of day for the respective radio transmission channels. The radio transmission channel can then also be selected by taking account of the charge parameter.
Further exemplary embodiments of the invention are explained in more detail below with reference to figures, in which:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.